Medical radiography is a well-known and extremely valuable tool for the early detection and diagnosis of various disease states of the human body. However, body cavities and the soft tissues of body organs and blood vessels exhibit so little absorption of X-ray radiation that radiographs of these body portions are difficult to obtain. To overcome this problem, radiologists introduce an X-ray absorbing method, i.e, a "contrast agent," sometimes referred to as a radiopaque, into such body cavities and tissues. Such contrast agents have been used in the X-ray examination of the human body almost from the days of Roentgen.
A wide variety of inorganic materials, such as bismuth subnitrate, bismuth subcarbonate, barium sulfate, and the like, have been proposed for use as contrast agents. Of these, barium sulfate is probably the most widely used.
In addition, various iodinated organic materials have been proposed for use as contrast agents, the iodine molecule representing an effective X-ray absorber. Among these are iodinated oils, such as ethyl iodophenylundecylate, used for myelography, and water-soluble, iodinated organic compounds used for X-ray visualization of the gastrointestinal tract. Water-soluble, iodinated organic compounds, however, can cause extremely severe side effects when used as a gastrointestinal contrast agent in dehydrated patients, especially infants. For this reason, these materials have become quite controversial and some radiologists no longer use such agents in the gastrointestinal tract. See Radiographic Contrast Agents, Miller and Skucas, page 169 (1977), University Park Press, Baltimore, Md. 21202.
More recently, certain water-insoluble, iodinated organic polymers have been proposed for use as radiographic contrast agents. For example, British patent specification No. 1,400,985 published July 23, 1975 discloses certain polymers which contain iodine-substituted aromatic groups. The polymers disclosed in this patent, although water-insoluble, readily swell in water to give a gel. The iodine content of actual polymers disclosed in this patent is typically in the area of about 20 to 30 weight percent, with the highest being 35 weight percent.
Although water-swellable iodinated polymers of the type described in British patent specification No. 1,400,985 may have certain utility, iodinated polymers which are both water-insoluble and non-water-swellable would be advantageous. Also, iodinated polymers having a higher iodine concentration than those specifically disclosed in this British patent would be desirable. For example, iodinated polymers with these properties could readily be added to water to produce a low viscosity radiographic contrast composition suitable for injection into the blood stream or other small organs and body cavities, without fear that the mixture would swell and cause a blockage. In addition, higher iodine concentrations could reduce both the intensity of X-ray radiation and the amount of contrast agent required to obtain good radiographic visualization.